Axial piston hydraulic pumps and motors commonly have a hardened valve plate stationarily positioned between a portion of the housing and a rotatable barrel. The valve plate has a plurality of kidney shaped ports extending therethrough for fluid communication between the piston bores of the barrel and intake and discharge passages in the head. The valve plates also typically have metering slots or grooves at the leading edge of the kidney ports for gradually increasing fluid communication between the piston bores and the respective intake and discharge passages in a manner which decreases hydraulic shock to alleviate noise and cavitation.
The valve plate of one such pump is made relatively thin so that the slots can be stamped to expedite the manufacturing process of the valve plates. A portion of the head forms the bottom of the slot. One of the disadvantages found with such thin valve plates is that the thickness of the valve plate is one of the factors determining the size of the orifice area of the metering slot. This limits the flexibility of controlling the orifice area as the piston bores open into the intake or discharge passages. It has also been found that high stresses are induced in the valve plate if the proper relationship of the plate thickness and slot size is not used.
Thus, it would be desirable to utilize the advantages of the thin valve plate design within a hydraulic axial piston unit while permitting a wider variety of metering slot geometries to be used for optimizing the operating characteristics of the axial piston unit.
The present invention is directed to overcoming one or more of the problems as set forth above.